H⁺-Pyrophosphatase Vacuolar Membrane under Lead Ion-Induced Stress

The effect of different concentrations of Pb²⁺ (0.1 µM−2 mM) on the functioning of vacuolar H⁺-pyrophosphatases of beetroot roots (Beta vulgaris L.) was studied. At the tissue level, in response to the action of 1 mM and 2 mM lead ions, there was an accumulation of lipid peroxidation products (diene conjugates) and an increase in the permeability of cell membranes, which indicates the development of oxidative stress. Evaluation of the functioning of H⁺-pyrophosphatases of tonoplast were determined according to the level of hydrolytic and transport activity of the enzyme. Stimulation of substrate hydrolysis catalyzed by H⁺-pyrophosphatase was observed in the presence of low concentrations of Pb²⁺. Metal concentrations above 500 μM inhibited the hydrolytic activity of the pyrophosphate-dependent enzyme. However, the level of transport activity was significantly stimulated in the presence of 1 mM Pb²⁺. Simultaneously, the conducted analysis of the qualitative and quantitative composition of fatty acids (FA) of total tonoplast lipids showed a reliably significant decrease in the content of oleic (C18:1(n-6)) and linoleic (C18:2(n-6)) FA under the action of 1 mM Pb²⁺. Lead ions at a concentration of 1 mM increased the amount of saturated fatty acids. It has been established that Pb²⁺ may affect the activity of H⁺-pyrophosphatases of tonoplast and the structure of cell membranes depending on concentration. It is possible that the identified changes are one of the mechanisms of adaptation to stress conditions caused by Pb²⁺.